Furnace carbon black is usually produced by a process in which a fuel is introduced in an axial or tangential direction of a cylindrical carbon black production furnace and burned; while transferring the formed high temperature combustion gas stream towards the downstream side, a hydrocarbon feedstock is introduced into the gas stream to let the reaction take place for the formation of carbon black; and then the formed carbon black-suspended hot gas stream is quenched to terminate the reaction. The formed carbon black is then collected and recovered by a collecting apparatus such as a cyclone or bagfilter.
Carbon black is used in various fields e.g. for producing rubber products, inks, coating materials, resin products, etc. The required properties such as the particle size and the aggregate size as well as the dibutyl phthalate absorption (hereinafter sometimes referred to as "DBP absorption"), the compression dibutyl phthalate absorption (hereinafter sometimes referred to as "compression DBP absorption") and their balance, as important indices for the structure, are delicately different depending upon the particular fields of applications. Therefore, it is necessary to control such physical property values to the desired levels depending upon the particular application, during the production stage of carbon black.
However, the thermal decomposition reaction for the formation of carbon black is complicated, and it has been very difficult to control the physical properties of carbon black to the desired levels within wide ranges and independently from one another and to efficiently produce carbon black.
For example, Japanese Unexamined Patent Publication No. 230677/1989 discloses a method for producing carbon black in which many and separate oil feedstock streams are supplied from separate portions to control the aggregate. In this method, the oil feedstock supply positions are changed to the upstream or the downstream of the gas stream in an oil feedstock injection zone of a conical shape to control the aggregate such as the aggregate size, whereby the structure is changed together with the change of the aggregate, and it is impossible to conduct the control of the aggregate and the control of the structure independently. Further, in this method, the cross sectional area in the reactor is not sufficiently utilized for mixing the high temperature gas and the oil feedstock, whereby the utilization efficiency of heat energy is low, and the yield of carbon black is low. This publication discloses nothing about the control of the structure balance represented by the compression DBP absorption/DBP absorption, which is an important characteristic of carbon black.
Further, Japanese Unexamined Patent Publication No. 190760/1989 discloses a method in which it is attempted to obtain a wider aggregate size distribution by injecting one of a plurality of oil feedstocks to a position where no increase of the compression DBP absorption will be brought about. However, the structure balance can not adequately be controlled by merely changing the position of the oil feedstock supply pipe of a later stage and the oil feedstock supply ratio between the earlier and later stages. Further, in this method, when the supply pipe for introducing the oil feedstock in the axial direction into the furnace is protected by quenching water, a loss of the heat energy generated in the first reaction zone will be brought about, and the production yield of carbon black will be low.
Thus, conventional methods for producing furnace carbon black used to rely only on the method of introducing the oil feedstock as a means to control the quality of the resulting carbon black, whereby it used to be difficult to sufficiently satisfy both aspects of the yield and wide control of the quality.